The present invention relates to a novel reflector structure in general and particularly to a strong, lightweight Cassegrain or Gregorian antenna for millimeter wavelength electromagnetic radiation.
When employed as transmitter antennas for millimeter wave electromagnetic radiation along an axis, the radiation feed faces forward on the axis and a small subreflector on the axis redirects the radiation onto a large forward looking primary reflector. In the Gregorian antenna, the subreflector is a concave ellipsoid and the primary reflector is a paraboloid. In a Cassegrainian system, the subreflector is a convex hyperboloid and the primary reflector is a paraboloid. The Cassegrainian system is superior because of its shorter overall length, and the Gregorian system is superior because the concave reflector surfaces are more easily fabricated.
The subreflector is supported in a fixed dimensional relationship with respect to the primary reflector to maintain the focal points of the primary and subreflectors in proper geometric alignment for successful antenna operation. Some examples in the prior art of the manner in which the subreflectors are mounted are shown in Ratkevich U.S. Pat. No. 2,942,264, Wild et al U.S. Pat. No. 2,945,233, Kibler U.S. Pat. No. 3,611,393, and Salmond et al U.S. Pat. No. 4,095,230. The Ratkevich patent shows the subreflector mounted upon an axial tube which is positioned in the radiation path. The other patents show the subreflector supported on legs which intercept a smaller portion of the projected area of the primary reflector. Except for the fact that there are at least three legs supporting the subreflector, no special structural interrelationship is taught.